Exercise 7.7. Modify the pattern finding program of Chapter 5 to take its input from a set of named files or, if no files are named as arguments, from the standard input.

Exercise 7.7. Modify the pattern finding program of Chapter 5 to take its input from a set of named files or, if  no files are named as arguments, from the standard input. Should the file name be printed when a matching  line is found?

#include <stdio.h>
#include <string.h>

#define MAXLINE 1000
#define NAME 20

FILE *in;
int except = 0;
int number = 0;
long lineno = 0;

int getline(char *line, int max);
void fstdin(char *line, char *pattern);
void ffile(FILE *fp, char *pattern, char *line, char *file_name);

/* find:  print lines that match pattern from 1st arg */
int main(int argc, char *argv[])
{
     char line[MAXLINE];
     char pattern[MAXLINE];
     char file[NAME];
;
     int c;
         
     while(--argc > 0 && (*++argv)[0] == '-')
        while(c = *++argv[0])
            switch(c)
            {
                case 'x':
                    except = 1;
                    break;
                case 'n':
                    number = 1;
                    break;
                default:
                    printf("find: illegal option %c\n", c);
                    argc = 0;
                    break;
            }
    if(argc < 1)
    {
        printf("Usage: find -x -n pattern file...\n");
        return 1;
    }
    else
        strcpy(pattern, *argv);
    if (argc == 1) // read from stdin
        fstdin(line, pattern //search in the string
    else
        while(--argc != 0) //get file`s name
        {
            strcpy(file, *++argv);
            if((in = fopen(file, "r")) == NULL)
            {
                perror(file);
                return 1;
            }
            else
            {
                ffile(in, pattern, line,file); //search in the file
                fclose(in);
            }
        }
    return 0;
}

/* ffile: search in the file */
void ffile(FILE *in, char *pattern, char *line, char *file_name)
{
    while(!feof(in))
    {
        fgets(line, MAXLINE-1, in);
        lineno++;
        if((strstr(line, pattern) != NULL) != except)
        {
            printf("%s\n", file_name);
            if(number)
                printf("%ld: ", lineno);
            printf("%s", line);
        }
    }
}
       
/* fstdin: search in the string from standart input */
void fstdin(char *line, char *pattern)
{
    while(getline(line, MAXLINE) > 0)
    {
        lineno++;
        if((strstr(line, pattern) != NULL) != except)
        {
            if(number)
                printf("%ld: ", lineno);
            printf("%s", line);
        }
    }
}

/* getline: read the string, return the length */
int getline(char *line, int max)
{
    if(fgets(line, max, stdin) == NULL)
        return 0;
    else
        return strlen(line);
}

Result: